Cook yellow onion, garlic, and thyme in the butter until tender.
Add the cauliflower florets and ¾ teaspoon salt and ¼ teaspoon pepper. Cook, covered, until the cauliflower is tender. Add chicken broth and cook for 20 minutes.
Add heavy cream and cook for 5 minutes. Transfer to a blender and puree until smooth. Garnish with chives and bacon.